The present invention relates to gradient index optical fibers and more particularly, to a two-row bundled array of such fibers, the fibers arranged in groups having square ends and identical lengths, the fiber lengths differing by group and forming a lens array which transmits an image of an object at an object plane to an image plane at magnifications other than unity.
Image transmitters comprising bundled gradient index optical fibers are known in the art. U.s. Pat. No. 3,658,407 describes a light conducting fiber made of glass or synthetic resin which has a refractive index distribution in a cross-section thereof that varies parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image of an object placed near one end. An assembly of fibers, in a staggered two-row array, transmits and focuses an image, at 1:1 magnification, of the object. The fiber lenses are produced under the trade name "SELFOC"; the mark is registered in Japan and owned by Nippon Sheet Glass Co., Ltd..
Numerous techniques are known in the art for manufacturing glass or plastic fibers with gradient refractive indices. These are usefully summarized in an article entitled "Gradient-index optics: a review" by Duncan T. Moore, Applied Optics, April 1, 1980, Vol. 19, No. 7, pp. 1035-1038.
It is also known in the art to construct a gradient index lens array capable of forming reduced or enlarged images of a document. Such a lens array is disclosed in U.S. Pat. No. 4,331,380 and in an article entitled "Reduction/enlargement gradient-index lens array" by James D. Rees and William Lama in Applied Optics, June 1, 1984, Vol. 23, No. 11, pp. 1715-1724. As disclosed in the patent, specific designs are provided for a one-row fiber array and for various two-row designs.
In one embodiment, shown in FIG. 13A of U.S. Pat. No. 4,331,380, a single row array is made by making all of the fibers with square-ended, rather than curved faces. "Square-ended" means that the end face of each fiber is planar and perpendicular to the fiber axis. This design requires each of the 200 or so gradient index fibers to be of a different specific length. The manufacturing of these fibers and their assembly is costly and time-consuming since each fiber must be formed separately at the required length and ground and polished separately.
It is therefore one object of the present invention to provide an improved embodiment of a reduction/enlargement gradient index lens array of a square-ended configuration. It is a further object to reduce the cost of manufacturing and assembly of the lens array. More specifically, the present invention relates to a reduction/enlargement lens array comprising a plurality of gradient index optical fibers each fiber having planar faces perpendicular to the fiber axis, with the fibers joined together to form at least a single row, said fibers formed into a plurality of groups, each fiber in each group having the same length with the fiber lengths in each grouping becoming progressively shorter with increasing distance from the center group of the lens array.